Switches are used to communicate between components of a processing environment. In particular, switches are used to route information between hosts of a processing environment and devices of that environment. There are many types of switches, but several popular switches used today are based on the Peripheral Component Interconnect (PCI) architecture, offered by PCI-SIG. These switches include PCI, PCI-X and PCI-Express (PCIe).
A PCI-based switch has a tree structure that enables the switch to be connected to one host. Specifically, the switch has one north facing port that enables the switch to be connected to the one host. The switch also has one or more south facing ports enabling the switch to be connected to one or more devices, such as disk controllers or other input/output devices. This tree structure places various restrictions on the switch, including its ability to connect to only one host.